The present invention relates to a method and an apparatus for cleaning methane fermentation digestion liquids, domestic wastewater, sewage, service water, culture pond water, wastewater produced by an activated sludge method, wastewater from food industries and the like.
Contamination of water environments is being made more and more serious by developments of industries and economy as well as rising of living levels of human lives. Eutrophication of water areas is made serious by nitrogen, phosphorus and the like which are contained in wastewater produced by agriculture and human lives. Furthermore, health of mankind is threatened by increase of organic matters, organic chlorine compounds, aromatic compounds, environmental hormones and the like contained in industrial wastewater. It is deemed difficult to completely treat such contaminants by a traditional water treating method such as a biological method. Under the present circumstances where legal regulations on environments are being strengthened, on the other hand, it is desired to construct an efficient wastewater treating system in order to maintain a stable ecosystem for a long time and preserve water resources having high safeties. It is therefore attempted to develop a new water treating technique which is to take the place of the biological method and an organic wastewater treatment by an electrochemical technique has been developed in recent years in particular.
A characteristic of the electrochemical treating technique lies in integration of technologies in different domains (for example, electronic engineering, catalytic technology, physical chemistry, microbiology and the like) and fusing techniques in different fields, thereby treating organic wastewater containing contaminants which are deemed hardly decomposable by the biological method.
The electrochemical treating technique is not only capable of removing solid matters and green powder contained in wastewater with a high efficiency without using a flocculant agent and suppressing a running cost at a low level but also produces sludge in an amount smaller than that of sludge produced by the biological treating method and allows the sludge to be reutilized as a fertilizer since the electrochemical technique does not use chemicals.
The electrochemical treatment has a floating function, an agglomerating precipitating function and an oxidizing function. The solid matters and the organic dissolved matters contained in soil water are removed by these three functions. Out of these functions, the oxidizing function is the most important and can be divided into direct oxidation and indirect oxidation. The direct oxidation oxidizes an organic matter directly on a surface of an oxidized metal by a catalytic function of the oxidized metal such as titanium oxide, tin oxide or the like. The indirect oxidation oxidizes with an xe2x88x92OH radial generated from water by anode discharge.
A reaction formula is:
H2O+M[ ]xe2x86x92M [xe2x88x92OH]+H++exe2x88x92xe2x80x83xe2x80x83(1)
A reaction formula of the organic matter by hydroxyl radicals is:
R+[xe2x88x92OH]xe2x86x92M [ ]+RO+H++exe2x88x92xe2x80x83xe2x80x83(2)
wherein a reference symbol M [ ] represents an active site on the surface of the oxidized metal and a reference symbol R designates the organic matter.
Ozone sending and irradiation with ultrasonic waves or electromagnetic ultrasonic waves are available as methods to generate oxygen radicals and hydroxyl radicals. Furthermore, though there has been developed a method which uses an optical catalytic reaction by titanium oxide, this method generates radicals in an amount small for a high input electric power, decomposes injurious materials with a low efficiency and requires a high cost of an apparatus. Furthermore, ozone is not effective for fresh water though ozone is deemed effective for sea water containing large amounts of bromine and manganese.
Furthermore, attention is paid to use of a transition metal such as cobalt, manganese or the like in combination with hydrogen peroxide. Though it is known the combination of the transient metal and oxygen peroxide generates radicals at an efficiency higher than that of ozone, this method require a delicate technique and final treatment of hydrogen peroxide in an outlet port since hydrogen neroxide has a variability for organisms high enough to be inhibited from being added to food.
It is known that the electrochemical treating method allows oxygen radicals and hydroxyl radicals to be generated with a lifetime of 10 xcexcs to 100 ms from existing water molecules when electrons enter pores existing in a surface of a material which is composed of fine particles of titanium oxide, tin oxide, ruthenium oxide, platinum or the like (see specification of Japanese Patent Application No. 11-68862). It is known that this radical oxidatively destructs organic substances including carbon sources and nitrogen sources as well as hardly decomposable aromatic substances contained in water.
It is indicated that a specific condition of an electric field to be applied between electrodes exists and it is necessary to prolong a time of contact between wastewater and a surface of a metal oxide for generation of the oxygen radicals and hydroxyl radicals with a high efficiency on the surface of the metal oxide, that it is necessary to clean surfaces of electrodes by transmitting ultrasonic waves when a large amount of floating suspended matters are contained in wastewater, and that a voltage, a current and an electric field frequency are governed by movements of electrons on the surface of the oxidized metal or the surface of the metal.
Since an invention described in the specification of the above mentioned application poses a problem that generation of superoxide radicals is insufficient in a high frequency region and excessive in a low frequency region, a problem that a current is unstable during treatment of wastewater containing a large amount of ions and the like, it is necessary to establish a treating method by combining a low frequency low current with a high frequency slight current and contrive to stabilize voltage pulse application when electric resistance of raw water changes during a treatment.
In order to solve the problems posed by the invention described in the specification of the above mentioned application, the applicant applied xe2x80x9cMethod and Apparatus for Cleaning Dissolved Organic Matters and Trace Amount of Injurious Materialsxe2x80x9d (Application 2000-29570 hereinafter referred to as xe2x80x9cspecification of preceding applicationxe2x80x9d) on February 2, Heisei 12.
An invention described in the specification of the preceding application disclosed a water purifying method characterized by coating a surface of a ceramic having a main body of feldspar or silicon with fine particles of titanium oxide, cobalt oxide, tin oxide, ruthenium oxide, iridium oxide, nickel oxide, iron oxide and vanadium oxide, fine metal particles of titanium, cobalt, nickel, silver and gold or a liquid consisting of a mixture these metals and a solution of the same kinds of metal salts, using as an electrode having a positive polarity the above described metal oxides or metals or the mixture thereof sintered in a temperature region of 800xc2x0 C. to 1500xc2x0 C. after a drying treatment and disposing an electrode which has a cathode made of platinum or titanium or stainless steel so as to be opposed to an anode for use of these electrode as a radical generating zone, continuously flowing wastewater between both the electrodes of these electrodes opposed to each other, causing pulse discharge between the electrodes under conditions of a voltage of 0.2 kV/cm to 20 kV/cm, an average current of 1 xcexcA/cm2 to 10 mA/cm2 and a frequency of 5 Hz to 50 MHz, thereby generating radicals by partial decomposition of water and oxidatively-reductively decomposing organic matters and intermediate products thereof dissolved in water.
Furthermore, the invention described in the specification of the preceding application disclosed a water cleaning apparatus for carrying out the above described water purifying method.
FIG. 9 shows an electrode section in which a anode and a cathode are disposed in opposition to each other. A reference numeral 51 in FIG. 9 represents a anode which has a groove extending in a direction of running water denoted by a reference numeral 52. The anode portion 51 is formed by coating a surface of a ceramic (non-metallic inorganic material including glass) having a main body of feldspar or silicon or a metal such as titanium with fine particles of titanium oxide, cobalt oxide, tin oxide, iridium oxide, nickel oxide, iron oxide and vanadium oxide, metal fine particles of titanium, cobalt, nickel, silver, gold and platinum or a liquid consisting of a mixture of the metals and a solution of the same kinds of metal salts, and sintering or welding the metals in a temperature region of 500xc2x0 C. to 1500xc2x0 C. A cathode 53 is made of platinum or titanium or stainless steel.
The anode 51 and a cathode 53 are disposed in opposition to each other and have a configuration in which the electrodes are enclosed by an outside cell 54. For a water treatment, water to be treated is sent from a lower portion (indicated by an arrow) to an upper portion of the outside cell 54 which is made of a high polymer resin such as acrylic resin, polyethylene resin or the like, and an angle xcex8 between bottom surfaces of both the electrodes opposed to each other and a foot of the cell is set at 30xc2x0 to 90xc2x0, thereby bringing most portion of contaminants in the water to be treated is brought into secure contact with the anode. The contaminants in the water to be treated are decomposed with a high efficiency by radicals which are generated from the anode 51.
FIG. 10 shown sectional configurations of water treating apparatuses: (a) showing a cylindrical circular truncated cone electrode type and (b) showing a truncated pyramid electrode type.
In FIGS. 10(a) and 10(b) showing the cylindrical circular truncated cone electrode type and the truncated pyramidal water treating apparatuses, a reference numeral 73 represents a raw water inlet port, a reference numeral 74 designates an anode electrode, a reference numeral 75 denotes a cathode electrode, a reference numeral 76 represents an overcoat (serving also as a cathode), a reference numeral 77 designates a treated water outlet port, a reference numeral 78 denotes a generated gas discharge port, a reference numeral 79 represents an electric insulating material and a reference numeral 79a designates a through hole formed in the insulating material 79 for passing raw water.
The truncated pyramid electrode type water treating apparatus shown in FIG. 10(b) uses electrodes which are formed by inserting the anode 74 made of metals and metal oxides into the overcoat 76 of the metallic cathode 75, placing a titanium plate, a platinum plate and a platinum bar at a center portion, and connecting these plates and bar to the overcoat portion.
The cylindrical circular truncated cone electrode type water treating apparatus shown in FIG. 10(a) has a configuration in which the water treating apparatus has a cylindrical or circular truncated conical structure having an angle xcex8 set at 30xc2x0 to 90xc2x0 between bottom surfaces of two anodes opposed to each other and a foot of a cell, an inside surface and an outside surface of this cylinder are composed of metal surfaces which are coated with powders of the above described oxidized metals, powders of the same metals or a mixture liquid consisting of a mixture thereof and salts of the same metals and sintered, a cathode having a form of a round bar or a square bar made of platinum, titanium or stainless steel is disposed at a center location of the cylindrical truncated cone, an outside of the cylindrical truncated cone is sealed with an overcoat container consisting of a metal container made of titanium, stainless steel or the like, a cathode is composed by disposing the above described overcoat container in a wastewater inlet port, a wastewater outlet port and a generated gas outlet port, and an inside surface and an outside surface of the cylindrical truncated cone are used as a radical generating zone so that organic wastewater is sent from a portion of having a large diameter inside the cylindrical truncated cone, comes out to a portion having a small diameter, flows again outside the cylindrical truncated cone in a direction reverse to that inside, and is oxidatively and reductively treated by generated radicals.
The truncated pyramidal electrode type water treating apparatus shown in FIG. 10(b) has a configuration in which a anode is configured as a flat plate having an angle xcex8 set at 30xc2x0 to 90xc2x0 between both bottom surfaces and roots of both electrodes opposed to each other, two flat plates positioned perpendicular to a thickness direction of the flat plate are composed of metal surfaces which are coated with the powders of the above described oxidized metals, the powders of the metals or the mixture liquid consisting of the mixture thereof and salts of the same metals and sintered, the two flat plates are disposed so as to be symmetrical with regard to a plane, further two side surfaces of the two flat plates which are not the oxidized metal surfaces are joined using a flat plate having a surface of titanium, stainless steel or the same metal on one side and composed as a truncated pyramid so as to uniformalize an anode voltage, an overcoat container is composed at a location symmetrical with a metal surface at a center of the truncated pyramid with regard to a plane by scaling outsides of a cathode electrode composed of a titanium plate, a stainless steel plate, a platinum net or platinum round bar and the truncated pyramid with a titanium or stainless steel container and a cathode is composed by disposing the above described overcoat container in a wastewater inlet port, a wastewater outlet port and a generated gas outlet port so that inside surfaces and outside surfaces of the two flat plates coated with the metal oxides serve as a radical generating zone, organic wastewater is sent from a portion having a large diameter or length inside the truncated pyramid, and organic matters and injurious materials contained in the wastewater coming out to a portion having a small diameter or length are oxidatively and reductively decomposed and treated by generated radicals while the wastewater flows again outside the truncated pyramid in a direction reverse to that inside.
Though the water treating apparatus and method described in the specification of the preceding application are epoch making water treatment apparatus and method, it has been found that these apparatus and method hardly allow a continuous operation since the continuous operation results in events such as accumulation of bubbles in a top section of the apparatus.
The present invention has an object to provide a water treating apparatus which is capable of operation continuously.
The present invention provides an apparatus for cleaning dissolved organic matters and a trace amount of injurious materials consisting of a anode which is formed by mixing clay and/or glass with 2 to 15% by weight of transition metals and 1 to 10% of oxidized transition metals, sintering the mixture within a range from 800 to 1500xc2x0 C. or coating a surface of a metal such as titanium with a mixture of fine particles of anatase type titanium oxide, tin oxide, ruthenium oxide and platinum as a glaze and sintering the mixture once again at a temperature from 580 to 980xc2x0 C.
Furthermore, the apparatus according to the present invention is characterized in that the above described anode is configured in a cylindrical form and an electrically conductive metal is fitted in an end of the anode.
Furthermore, the apparatus according to the present invention is characterized in that at least an electrically conductive metal is inserted in parallel with an axis of the above described cylindrical anode.
Furthermore, the apparatus according to the present invention is characterized in that a pulse voltage and a current are applied to the above described electrically conductive metal.
Furthermore, the apparatus according to the present invention is characterized in that a cathode is disposed at a center of the above described cylindrical anode. Furthermore, the apparatus according to the present invention is characterized in that the above described anode and the above described cathode are set in a condition where the anode and cathode are submerged in water and connected to an oscillator which oscillates an average current density of 0.1 xcexcA/cm2 to 10 mA/cm2 at a frequency of 5 Hz to 50 MHz and a voltage of 0.2 kV/cm to 20 kV.
Furthermore, the apparatus according to the present invention is characterized in that raw water is flowed downward from an upper portion to a lower portion of the side wall of the above described anode and oxidized and cleaned by various kinds of active species (radials) generated between the above described cathode and anode.
Furthermore, the apparatus according to the present invention is characterized by being composed of a anode configured in a form which has a rectangular or truncated pyramidal concave portion.
Furthermore, the apparatus according to the present invention is characterized in that a transition oxidized metals is sintered at 580xc2x0 C. to 980xc2x0 C. in the concave portion of the above described anode and electrically conductive metal plates are formed on both sides of the electrode as a cathode by way of an insulating material.
Furthermore, the apparatus according to the present invention is characterized in that the above described anode measures 5 to 10 mm thick by 5 to 100 cm wide by 10 to 70 cm high.